1. Field of the Invention
The present invention relates to cinema sound systems and more particularly to mid-frequency range loudspeaker systems.
2. Related Art
When designing a cinema or theater loudspeaker system, it is desirable to provide uniform or consistent loudness and full mid-frequency range sound coverage to the seating locations in the cinema. Further, the perceived sound source needs to sufficiently coincide with the images projected on the screen, while operating with an efficiency that keeps the total audio amplifier power requirements within practical limits.
One design approach for cinema loudspeakers is the use of conventional horns or waveguides and drivers. One drawback with the use of conventional horns or waveguides is that frequency pattern control of conventional horns or waveguides require a relatively large mouth and overall size to provide the required directivity. For example horns of conventional designs are required to be about four to five feet in depth to achieve the required pattern control at frequencies in the order of 250 Hz. Conventional horns designs are therefore generally undesirable because they occupy a large area behind the cinema screen, decreasing the amount of usable cinema space.
Another design approach for providing cinema sound is with array loudspeakers. An array of loudspeakers may have multiple speakers with selective frequency response ranges similar to a home speaker unit with a high, mid, and low-range speaker. However, the unusual degree of beam width confinement and control required for successful implementation of an array of loudspeakers to function as a unified signal source presents additional design challenges. Furthermore, array loudspeakers are unable to compensate for phases between the different loudspeaker signals and are unable to control the vertical off-axis angle at which the summation between the signals is greatest.
Thus, a need exists for a loudspeaker system that is smaller than a conventional horn design yet provides the frequency pattern control of the horn design and the selective frequency responses of array loudspeakers to satisfy the size, coverage and power requirements of a cinema or theater.